The object of this project is to describe the key features of embryonic development of nervous system. The features which will be followed include (1) how and when the characteristic adult morphology of identified neurons arises; (2) how and when the adult physiological characteristics of identified neurons arise; (3) how and when known synapses between identified neurons arise; (4) the order of establishment of synapses in a neural circuit; (5) the major general events in laying down the groundplan of the nervous system; and (6) the cell lineages through which identified neurons arise from possibly identifiable neuroblasts. A description of these features should provide considerable insight into mechanisms of differentiation. In experiments based on this description, it should be possible to test hypotheses about such developmental mechanisms by experimental manipulation of the embryo.